1. Field of the Invention
The present invention relates generally to a work machining method such as machine cutting and grinding and an apparatus for supplying mist which may be used in the method.
2. Description of the Prior Art
To dissipate heat generated by contact between a workpiece and a machine tool during machine cutting or grinding, conventionally a liquid is delivered from a water-supply nozzle extending toward the machining position. For example, in a machining center (a complex machine tool) as shown in FIG. 7, a tool holder 2 is installed on the lower end of a spindle (not shown) of a body 1 and a tool connecting axis 3 is to be engaged with a machining tool 4, to which a water supply nozzle or an air supply tube 5 extends from the body 1. However, in machining using a large-scale stand type machine tool like this machining center, there may be a situation where machining performance is adversely deteriorated because water or debris easily accumulates inside a machined recess. In addition, when machining by intermittently contacting a carbide machining tool with a workpiece, the temperature rises on the machining point of the cutting edge due to generated heat while the cutting edge simultaneously is being cooled by the liquid delivery. Thus, repeated sudden thermal changes may cause the so called "chipping" phenomena or cracks.
For this reason, liquid is sprayed in a mist toward a workpiece and a machining tool so as to impart lubricity instead of liquid delivery. According to this method, the inconvenience of water accumulation within the recess may be avoided or the chipping phenomena by sudden cooling may not be caused. However, this method has problems in that lubricity is not sufficient when using water as the liquid for the mist, and in that the cooling effect is not sufficient when using oil as the liquid for the mist. For example, an oil feeder and an oil feeding method for supplying the oil in a mist form are proposed by TOKKAIHEI 9-141537.
Therefore, as a method to realize cooling effect and lubricity by ejecting liquid in a mist form for machining a workpiece has been proposed by TOKKAIHEI 6-320384. According to this method, instead of only one kind of a liquid being ejected in a mist form, two or more kinds of liquids are mixed and ejected in a mist form. An ejection nozzle 51 as shown in FIG. 8 is connected to an end of an air supply tube 5 as shown in FIG. 7. In nozzle 51 two branch liquid supply tubes 52a, 52b are branched away from a liquid supply tube 52 connected to one side (the right side in FIG. 8) of the ejection nozzle 51. The branch tube 52a supplies water while the other branch tube 52b supplies oil. When compressed air is supplied from the air supply tube 5, as shown by an arrow P in FIG. 8, a piston 54 held by a compression spring 53 is pushed toward the opposite side (left side in FIG. 8) in the nozzle 51 so that a liquid passage 55 connected to the liquid supply tube 52 is opened. Consequently, water and oil are sprayed out in mixed fine particles from the very small outlets of nozzles 56 and 57 which are branched off toward the right and left, respectively.
In machining a workpiece in this machining center, when compressed air is supplied to the air supply tube 5 and also water and oil are supplied to the liquid supply tube 52, a liquid mixture of water and oil is ejected from the ejection nozzle 51. The water and oil, which coexist in fine particles, collide with a surface of a workpiece to be machined as well as with a surface of a machining tool to be pressed on the workpiece. The oil particles mainly increase lubricity while water mainly dissipates the heat produced during machining.
However, according to the above method, in mixing the oil and water, the quality of thus obtained liquid mixture may deteriorate, resulting in insufficient lubricity. Further, it is difficult to mix water and oil, resulting in insufficient mixing in the mixture liquid. As a result, it is difficult to impart both the cooling effect and lubricity at the same time between the surface of the workpiece and the surface of the machining tool. Still further, since the water and oil are injected together into the nozzle with the injection of compressed air, it is not possible to separately regulate the injection pressures of each of the compressed air, water and oil.
In view of the foregoing, it is an object of the present invention to provide a method for machining workpieces and an apparatus for supplying mist used therein, whereby quality of the liquids may not deteriorate, a cooling effect and lubricity are rendered at the same time between the part to be machined and the machining part, and the injecting pressure of each of the compressed air, water and oil can be separately regulated.